A. Field of the Invention
This invention relates generally to the field of proportional control valves.
B. Prior Art
It has been widely known in many prior proportional control valves to use mechanical feedback. Specifically, in such valves, a torque motor has been used with a flappernozzle arrangement. However, this arrangement has left much to be desired particularly in view of the relatively high cost. In addition, such torque motors have operated on very low level forces and thus substantial amplification has been required between the low level pilot and the servo valve. Further, with low level forces, small orifices have been used which tended to easily clog and cause the valve to become inoperable. The orifices were not self cleaning because of the low level forces. A further problem has been in balancing the orifices which becomes critical because of the high amplification. A small piece of dirt lodging in one of the orifices would result in large change in the output of the servovalve.
Other known proportional control valves have left much to be desired in simplicity of operation, reliability and cost. For example, see the following patents U.S. Pat. Nos. 2,993,477; 3,434,390; 3,742,980; 3,749,128; 3,757,822; 3,799,202.
Accordingly, an object of the present invention is a feathering valve assembly which exhibits important characteristics of a proportional control valve but at substantially lower cost with high reliability and simplicity of operation.